The invention relates generally to hydrogen-selective membranes and devices that form and/or purify hydrogen gas, and more particularly to methods for forming hydrogen-selective membranes, hydrogen-selective membrane modules, hydrogen purifiers and fuel processors.
Purified hydrogen is used in the manufacture of many products including metals, edible fats and oils, and semiconductors and microelectronics. Purified hydrogen is also an important fuel source for many energy conversion devices, such as fuel-cell systems, and especially proton-exchange-membrane fuel-cell (PEMFC) systems.
Hydrogen gas streams may be produced by fuel processors that produce hydrogen gas by chemically reacting one or more feed streams. These fuel processors often require that the initial hydrogen stream be purified before the stream is suitable for use in a particular application, such as a feed stream to a fuel cell.
An example of a suitable fuel processor is a steam reformer, which produces hydrogen gas by reacting a hydrocarbon or alcohol with water. Other examples of suitable fuel processors produce hydrogen gas by autothermal reforming, partial oxidation of a hydrocarbon or alcohol vapor, by a combination of partial oxidation and steam reforming a hydrocarbon or an alcohol vapor, by pyrolysis of a hydrocarbon or alcohol vapor, and by electrolysis of water. Examples of suitable fuel processors and fuel cell systems incorporating the same are disclosed in U.S. Pat. Nos. 5,861,137, 5,997,594 and 6,376,113, the disclosures of which are hereby incorporated by reference.
Hydrogen-selective membranes formed from hydrogen-permeable metals, most notably palladium and alloys of palladium, are known. In particular, planar palladium-alloy membranes have been disclosed for purifying hydrogen gas streams, such as hydrogen gas streams produced by steam reformers, autothermal reformers, partial oxidation reactors, pyrolysis reactors and other fuel processors, including fuel processors configured to supply purified hydrogen to fuel cells or other processes requiring high-purity hydrogen.
To be economical, palladium and palladium-alloy membranes must be thin. For example, planar membranes are typically approximately 0.001 inches thick. However, forming an extremely thin membrane tends to become more expensive from a manufacturing standpoint as the thickness of the membrane is reduced. Furthermore, extremely thin membranes are subject to wrinkling during assembly into a membrane module containing one or more hydrogen-selective membranes. A membrane that has one or more wrinkles is subject to premature failure due to stress fractures forming at the wrinkle. When such a failure occurs, impurities that otherwise would be unable to pass through the membrane can now pass through the membrane, thereby reducing the purity of the product hydrogen stream and potentially damaging the fuel cell stack or other hydrogen-consuming device with which the purified stream is used.
The present invention is directed to membrane modules that contain one or more hydrogen-selective membranes, methods for preparing the same, and hydrogen purification systems, fuel processors and devices containing the same. In some embodiments, the membrane modules include one or more hydrogen-selective membranes supported on a support or screen structure, of which a variety of embodiments are disclosed. In some embodiments, the membrane or membranes are adhesively mounted on the screen structure during assembly. In some embodiments, the screen structure includes a plurality of screen members adhesively mounted together during assembly. In some embodiments, the screen structure includes a coating. The present invention is also directed to methods for reducing the thickness of hydrogen-selective membranes.